This invention relates to aviation power plants and to the means for preventing the icing of surfaces in the air intake opening of an aircraft engine.
Various more or less effective means for minimizing the accumulation of ice on exposed intake surfaces of aviation power plant are known. Deicing apparatus is particularly desirable for protection of the air intake opening of a gas turbine engine of the type comprising a turbine driven compressor, which is operable to draw large volumes of air from the atmosphere through the forward directed intake opening for delivery under pressure to the fuel combustion apparatus of the engine.
A conventional gas turbine engine comprises a streamlined cylindrical outer casing which may be mounted in or on the fuselage of an aircraft, and which is mounted to present minimal frontal area and drag during operation of the plane at high speed. Supported within the outer casing is an inner casing which forms an annular passageway through the engine from a forward directed air intake to a rearward directed exhaust. Air entering the intake opening is compressed and delivered to a combustion chamber. Hot gases issuing from the combustion chamber are then expanded through the turbine and discharged through the exhaust as a jet to provide propulsive thrust or to drive a fan.
In order to insure proper distribution of intake air flowing to the compressor and to turn the air to the proper angle so that the air strikes the compressor vanes at the proper angle, a plurality of inlet guide vanes are used. During the operation of the engine large quantities of air are drawn through the air intake and past the guide vanes, with the result that deposits of ice tend to accumulate on the exposed surfaces.
The prior art discloses many anti-icing systems for preventing the accumulation of ice on the inlet guide vanes. A simple and practical deicing or anti-icing system for an aircraft gas turbine engine uses hot gases piped from a point aft of the compressor to a manifold surrounding the guide vanes or other elements exposed to the air intake. For example, Burgess U.S. Pat. No. 2,718,350 discloses a system which deices by bleeding compressor air and supplying it to the interior of hollow inlet guide vanes. In other systems such as Frost U.S. Pat. No. 2,680,345 a special combustion system is used to supply hot gases to the interior of the vanes. In Larson U.S. Pat. No. 3,341,114 hot gases applied to the interior of the guide vanes cause internal corrugations to flex and therefore aid in the breaking up of ice forming on the surfaces of the inlet guide vanes. In Hodges et al U.S. Pat. No. 2,634,049, the gas turbine exhaust gases are used to heat various forms of inlet guide vanes.
The prior art also teaches deicing by inducing sonic or ultrasonic vibrations within the inlet guide vane. As pointed out in Levin U.S. Pat. No. 3,779,488 a number of deicing systems functioned by building up ultrasonic or audio frequency oscillations on the surface of the vane. These oscillations were induced by generating electrical oscillations and converting those oscillations to mechanical vibrations. Levin claimed to have improved the prior art systems by making a more efficient oscillator.